Self-adjusting tappet



Patented Feb. 1, 1949v SELF-ADJUSTING 'TAPPET Joseph Norman Paquin,Euclid, Ohio, assignor to The Weather-head Company, Cleveland, Ohio,

a corporation of Ohio Application May 2, 1945, Serial No. 591,577

My invention relates to tappets' and concerns particularly valve tappetsfor gas engines.

One of the objects of my invention is to provide a self-adjusting valvetappet. p

The principal object of the invention is to compensate for variations inlength of valve stems, valve rods or other operating rods forcommunicating reciprocating motion.

It is an object of the invention to overcome lost motion in internalcombustion engines and to avoid variation of period and timing of valveopening as well as to avoid noise and wear of loose parts.

3 Claims. (Cl. 123-90).

Another object is to compensate for the effect of variations intemperature on length of the valve rod, and to avoid undue loss ofefiiciency of an internal combustion engine when the engine is stillcool.

More specifically, an object is to provide for close adjustment oftappets while the engine is cool as well as when the engine is heatingup.

A further object is to provide self elongation and contraction of atappet without external connections or controls.

Still another object is to provide reliable, selfcontained, hydrauliccompensation for tappets in which paths for uncontrolled leakage ofhydraulic fluid are eliminated.

A further object is to provide hydraulic compensation for a tappet inwhich passage of hydraulic fluid from one part to another of the tappetis limited to pre-determined means for metering the flow.

An object of my invention is to provide a self adjusting tappet whichwill take up clearance between the valve stem and cam regardless of theoperating temperature of the engine.

Still another object of my invention is to provide improved sealingarrangements for movable pistons and plungers.

Still another object is to provide improved methods and apparatus forproducing an orifice or opening of accurately determined, very minute,cross-section in a thick wall, sheet, plate or the like. It is, also,anobject to provide an improved arrangement for reducing the size oforifices.

Other and further objects, features, and advantages of my invention willbecome apparent as the description proceeds.

In carrying out the invention in accordance with a preferred embodimentthereof, a tappet is formed in -two relatively movable parts; one

comprising a hollow cylinder, and the other a hollow piston adapted toslide in the cylinder with a hydraulic fluidsuch as oil contained in thecylinder and in a reservoir formed in the piston. Means are providedfor' causing the hydraulic fluid to be transferred from the reservoir tothecylinder, tending to push the piston out from the cylinder and toextend the tappet for taking up any clearance occurring between thevalve stemand the cam.

The piston has an inner transverse wall or base with an opening thereinfor enabling the fluid to be transferred between the reservoir in thepiston and the cylinder. Preferably a relatively minute opening ororifice is utilized which is formed by drilling a hole in the base ofthe piston and inserting a plug which has been flattened on one side toleave an orifice. The orifice is preferably near a side wall of thepiston for the purpose of introducing turbulence and coolin effects inthe hydraulic fiuid or oil.

Suitable means such as liners or sac-like membranes of rubber. or othersuitable flexible material are provided for the piston reservoir and thecylinder to overcome any tendency for leakage of the hydraulic fluid, ora seal may be provided between the cylinder and the piston.

A better understanding of the invention will be afiorded by thefollowing detailed description considered in conjunction with theaccompanying drawing, and the scope of the invention will be set forthin the claims.

In the drawing:

Fig. 1 is a longitudinal sectional view of an embodiment of myinvention;

Fig. 2 is a fragmentary sectional view of a portion of the base of thepiston of the tappet shown in Fig. 1;

Fig. 3 is a fragmentary sectional view representing a portion of theapparatus as cut by a plane 3-3 indicated in Fig. 2; and

Fig. 4 is a sectional view of a tappet employing flexible sacs in thecylinder and the piston reservoir.

Like reference characters are utilized throughout the drawing todesignate like parts.

Referring to Fig.- 1, the arrangement shown therein by way ofillustration comprises a portion of a casing I I for an internalcombustion engine, such as a gasoline engine, for example, having aconventional poppet valve l2 controlled by valve stem I 3 or controlledby valve rod represented by the rod i3 slidable in a suitable guide orbushing I4. A valve spring I5 is provided for normally closing the valvei3 by moving the stem l3 in a downward direction. A tappet I6 isprovided for transferring the action of a valve-operating cam H to thevalve rod i3. As in conventional constructions, the tappet l6 has ahardened lower surface I3 adapted to ride on the cam I! and a hardenedupper surface I9 adapted to contact the lower end 2! of the rod N. Thetappet I 6 comprises two parts 22 and 23 which are relatively movablelongitudinally although the extent of movement required is relativelylimited. One of these parts, for example, the part 22, takes the form ofa hydraulic cylinder, and the other which is the part 23 takes the formof a hollow piston. A suitable relatively incompressible hydraulic fluidsuch as oil, for example, is provided for filling the cylinder 22, and areservoir 25 formed in the piston 23 for supplying oil to the cylinder22 to extend the tappet length.

The piston 23 and the cylinder 22 areeach closed at the outer end, andthe piston 23 is pro- 4 between the com I? and the valve rod l3, thespring 36 forces the piston 35 downward expelling hydraulic fluid fromthe reservoir 25 through the orifice 21 into the cylinder 22. Thisaction extends the tappet l6 and takes up any clearance. Upon thepressure stroke of the cam I1,

' the cam follower I8 is lifted, and the oil pressure vided with aninner transverse wall 26, which 4 may be at the base of the piston 23.There are means permitting the restricted passage of the hydraulic fluidor oil between the reservoir and the cylinder 22. For this purpose aminute passageway 21 is formed in the transverse wall 26, permittingmetered or accurately controlled transfer of oil to the reservoir 25from the cylinder 22.

Suitable sealing means are provided for preventing leakage of oil fromthe cylinder 22 ex cept through the orifice 21 and for, likewise,preventing escape of oil from the reservoir 25 except through theorifice 21 into the cylinder 22. For example, as illustrated in Fig. 4,liners 26 and 23 may be provided in the cylinder 22 and the reservoir 25respectively for sealing the oil in the respective chambers. The liners28 and 29 are preferably composed of a suitable flexible rubberlikematerial such as rubber or composition sheeting. The liner 28 is formedas a continuous sac with an opening or mouth having a bead adapted tosnap into an annular groove 32 around the lower edge of the piston 23for sealing the sac 28 to the lower surface of the piston 23. The liner29 comprises a sac having an opening or mouth 33 with a lip 34 aroundthe orifice 2'! sealed to the upper surface of the transverse pistonwall 26 preferably by cementing and bonding by vulcanization.

Suitable means are provided for tending to cause transfer of oil fromthe reservoir 25 to the cylinder 22. Such means may take the form of anarrangement for resiliently expelling oil from the reservoir 25. Forexample. a pressure plate or plunger 35 maybe provided above the upperend of the reservoir liner or sac 29 with a biasing spring 36 serving topress the plunger 35 downward for expelling oil from the reservoir 25.Preferably, a cap 31 is provided for closing the upper end of the hollowpiston 23 and facilitating the assembling of the apparatus with thespring 36 in the space between the cap 31 and the plunger.

The piston 23 is arranged to be slidable within the cylinder 22 at theopen or upper end thereof. However, the required extent of movement isrelatively slight inasmuch as the apparatus is originally designed tooccupy very nearly the entire space between the cam if and the lower endof the push rod 2|. The tolerances or variations in clearance to betaken care of represent relatively slight movement of the piston 23within the cylinder 22, consequently relatively little flexing of theupper portions of the liners or the sacs 28 and 29 is required.

The spring 36 is preferably weaker than the valve spring 15. If thereshould be any clearance forces the piston 23 up together with thecylinder 22.

The rate of fiow of the hydraulic fluid through the minute orifice 21 isrestricted by the size of the orifice, and prevents any appreciablecon.- traction of the tappet. Nevertheless, gradual contraction of thetappet is permitted in case it should be necessary in order to enabletight sealing of the valve l2 when changes of temperature of the engineor operating conditions tend to increase the length of the valve rod orpush rod l3 in relation to other parts of the structure.

It will be observed that the cam i1 is so constructed that the power orpressure stroke exists only during the time required for a quarterrevolution of the cam H to be made; namely, during the time required forthe cam to advance from the point 38 to the point 33 in contacting thecam follower 16. During this time the cam pressure opposes the pressureof the spring 36 and there is a tendency for transfer of 011 backthrough the orifice 21 from the cylinder 22 into the reservoir 25.

The cam follower I3 is permitted to fall during the time required forthe cam l! to rotate through the from the point 39 to the point 40. Thecam follower dwells on the base circle during the of rotation from thepoint 60 to the point 38. Consequently, during three-quarters of therevolution of the cam I! the springpressed piston 35 is free to expel011 from the reservoir 25 into the cylinder 22 for the purpose of takingup any clearance. Thus the cylinder 22 is at all times kept adequatelyfilled to extend the tappet I 6 the amount required to overcome anyclearance between the push rod l3 and the cam l1. Thus the tappet l6constantly hunts for its correct length and any changes in operatingconditions, temperatures, or wear of the parts which might causeclearance to increase or decrease in a tappet of fixed length arecompensated by the self-compensating or self-adjusting tappetarrangement.

For obtaining the requisite sturdiness and durability of the apparatus,it stands to reason that the inner-transverse wall or base 26 of thepiston 23 will be of relatively heavy construction or thick incomparison with the diameter of a round orifice which would besufliciently small. To drill an orifice of such minute diameter throughthe thick wall 25 would be relatively difficult. Accordingly, for thesake of increasing the precision with which the orifice cross-section isfixed and the ease with which the orifice may be made, and also makingit possible to produce much finer orifice than would otherwise bepossible, I have found that I may drill a relatively large opening suchas an opening 42 in the wall 26 and insert therein a plug 43 in theshape of a right circular' cylinder of the same external diameter as theinternal diameter of the opening l2. However, the plug 43 is flattenedon one side 44 by removing a segment thereof by grinding, e. g., so asto leave a minute space having a cross-section corresponding to theshape of a circular segment which forms the actual orifice 21. In orderto secure the plug 43 permanently within the opening 42 the edges l5 ofthe openmg "are preferably peened over after the plug.

42 has been inserted in opening 42. The construction of the plug 48 andthe orifice 21 are shown in detail in Figs. 2 and 3. As shown in Fig. 1,the orifice 21 is not only at one side of the opening 21 but ispreferably also eccentric with respect to the piston22 and the cylinder22,.

lower surface 46 of the piston 23 being reduced in diameter sufficientlyto provide space for the wall of the sac 28. However, my invention isnot limited to the specific construction disclosed in F 8. 4. If desiredO-ring seals may be employed. Such a seal comprises a ring 41 composedof compressible material such as rubber or synthetic compound fltting inan annular groove 48, as illustrated in Fig. 1. Preferably the groove 48has a greater axial length than depth and the cross-section of thering47 is less than the crosssection of the groove 48, but its uncompresseddiameter is greater than the depth of the groove 48, so that a rollingeflect is produced when relative motion takes place between the piston28 and the cylinder. 22.

While I have described my invention as em-' bodied in concrete form, andas operating in its speciflc manner in accordance with the provisions ofthe patent statutes, it should be understood that I do not limit myinvention thereto since various modifications thereof will suggestthem-'- selves to those skilled in the art without departing from thespirit of my invention, the scope of which is set forth in the annexedclaims.

What is claimed is:

1. A tappet comprising in combination a crlln v 6 the closed-end of thepiston, flexible sacs carried by 'said piston with mouths sealed onopposite sides of the inner end wall of said piston around a 1 saidopening, and fluid within said sacs.

2. A- sealed self adjusting tappet unit comprising a cylinder, a hollowpiston in said cylinder having an inner wall, fluid sealing means toprevent flow of fluid from said cylinder past said piston, orifice meansin the inner end wall of said piston, a sac in said piston with itsmouth sealed against said inner piston wall, fluid in said sac, plungermeans in said piston engaging an outer wall of said sac, and resilientmeans cooperating with said plunger means arranged to cause fluidtransfer from said sac to said cylinder through the oriflce. and fluidin said cylinder.

3. A sealed self adjusting tappet unit comprising a cylinder, a hollowpiston in said cylinder,

der open at one end, a hollow piston within said cylinder projectingfrom the open end of the cylinder, said piston having a closed outer endand an inner end wall with a constricted opening therein, a plunger insaid piston, means for exertmg force on said plunger in a direction awayfrom fluid sealing means to prevent flow of fluid from said cylinderpast said piston, orifice means in the inner end wall of said pistonarranged to provide for fluid transfer between said cylinder and pistonin either direction, a first sac in said piston with its mouth sealedagainst said inner piston wall, fluid in said sac, a second sac in saidcylinder with its mouth sealed to said piston end wall; plunger means insaid piston and engaging said first sac arranged to cause fluid transferto .the

sac in said cylinder through the orifice, and fluid in said sacs.

JOSEPH NORMAN PAQUIN.

REFERENCES crrnn The following references are of record in the tile ofthis patent:

- mm'sn s'rA'rEs rams Number Barr Feb. 5, 1948

